U.S. patent number 4,021,327 [Application Number 05/572,832] was granted by the patent office on 1977-05-03 for reinforced cation permeable separator.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to Walther Gustav Grot.
United States Patent |
4,021,327 |
Grot |
May 3, 1977 |
Reinforced cation permeable separator
Abstract
A cation permeable separator containing a polymer with ion
exchange sites is reinforced with supporting fibers introduced into
a polymer matrix in a fabric which also contains sacrificial fibers
that are subsequently removed. In electrolysis of brine, the use of
this type of reinforced cation permeable separator positioned
between anode and cathode compartments of an electrolytic cell has
resulted in increased electrical efficiency and/or decreased
voltage.
Inventors: |
Grot; Walther Gustav (Chadds
Ford, PA) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
24289545 |
Appl.
No.: |
05/572,832 |
Filed: |
April 29, 1975 |
Current U.S.
Class: |
204/296 |
Current CPC
Class: |
B32B
5/08 (20130101); B32B 27/12 (20130101); B32B
27/304 (20130101); C08J 5/2237 (20130101); C08J
5/2281 (20130101); B32B 27/322 (20130101); B32B
2262/0238 (20130101); B32B 2309/02 (20130101); B32B
2260/021 (20130101); C08J 2327/12 (20130101); B32B
2262/062 (20130101) |
Current International
Class: |
C08J
5/20 (20060101); C08J 5/22 (20060101); C25B
013/08 () |
Field of
Search: |
;204/296 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Edmundson; F.C.
Claims
What is claimed is:
1. A cation permeable separator substantially impervious to
hydraulic flow of liquid comprising a fluorine-containing polymer
with a plurality of sulfonyl groups present as ion exchange
sites,
said sulfonyl groups being contained in side chains and being
attached to individual carbon atoms to which are attached at least
one fluorine atom,
said separator containing support fibers and containing voids which
are formed by the removal of sacrificial fibers, said supporting
fibers and sacrificial fibers initially comprising a fabric prior
to formation of said voids.
2. The cation permeable separator of claim 1 wherein said
fluorine-containing polymer is perfluorinated.
3. The cation permeable separator of claim 2 wherein said
fluorine-containing polymer is a copolymer formed from
tetrafluoroethylene and
perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride).
4. The cation permeable separator of claim 1 wherein said support
fibers comprise a perfluorinated polymer.
5. The cation permeable separator of claim 4 where said
perfluorinated polymer is made from one or more monomers selected
from tetrafluoroethylene, hexafluoropropylene and perfluoro(alkyl
vinyl ether) with an alkyl of 1 to 10 carbon atoms.
6. The cation permeable separator of claim 1 in the form of a film
with a thickness of no more than 30 mils.
7. The cation permeable separator of claim 6 wherein said thickness
is no more than 20 mils.
8. The cation permeable separator of claim 7 wherein said thickness
is no more than 12 mils.
9. A cation permeable separator comprising a fluorine-containing
polymer with a plurality of sulfonyl groups present as ion exchange
sites,
said sulfonyl groups present as ion exchange sites being contained
in side chains and being attached to individual carbon atoms to
which are attached at least one fluorine atom,
said separator containing a fabric comprising supporting fibers and
sacrificial fibers.
10. A film comprising a fluorine-containing polymer with a
plurality of sulfonyl groups present as --SO.sub.2 X with X
defining chlorine or fluorine,
said sulfonyl groups being contained in side chains and being
attached to individual carbon atoms to which are attached at least
one fluorine atom,
said film containing a fabric comprising supporting fibers and
sacrificial fibers.
11. The film of claim 10 where X defines fluorine.
12. A microporous cation permeable separator capable of allowing
hydraulic flow of liquid comprising a fluorine-containing polymer
with a plurality of sulfonyl groups present as ion exchange
sites,
said sulfonyl groups being contained in side chains and being
attached to individual carbon atoms to which are attached at least
one fluorine atom,
said separator containing supporting fibers and containing voids
which are formed by the removal of sacrificial fibers, said
supporting fibers and sacrificial fibers initially comprising a
fabric prior to formation of said voids.
13. The cation permeable separator of claim 12 wherein said
fluorine-containing polymer is perfluorinated.
14. The cation permeable separator of claim 13 wherein said
fluorine-containing polymer is a copolymer formed from
tetrafluoroethylene and
perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride).
15. The cation permeable separator of claim 12 wherein said support
fibers comprise a perfluorinated polymer.
16. The cation permeable separator of claim 15 where said
perfluorinated polymer is made from one or more monomers selected
from tetrafluoroethylene, hexafluoropropylene and perfluoro(alkyl
vinyl ether) with an alkyl of 1 to 10 carbon atoms.
17. The cation permeable separator of claim 12 in the form of a
film with a thickness of no more than 30 mils.
18. The cation permeable separator of claim 17 wherein said
thickness is no more than 20 mils.
19. The cation permeable separator of claim 18 wherein said
thickness is not more than 12 mils.
Description
BACKGROUND OF THE INVENTION
The present invention relates to cation permeable separators which
are particularly useful to divide anode and cathode compartments of
an electrolytic cell.
In recent years development of cells which are useful for
electrolysis of an alkali or alkaline earth metal halide solution
by use of a cation permeable separator containing a polymer with
ion exchange sites has been undertaken. These polymers have been
made to have thermal and chemical stability necessary to
manufacture highly reactive chemicals, e.g., electrolysis of brine
to produce chlorine and caustic. In addition to chemical and
thermal stability of the polymer, the electrolytic cell should be
able to operate at a high cell efficiency and low power
consumption.
From an economic standpoint recently developed electrolytic cells
containing new types of cation permeable separators must be able to
compete with proven electrolytic cells which are commercially such
as, diaphragm cells, which employ asbestos as a separator, and
mercury cells.
SUMMARY OF THE INVENTION
The present invention is directed to an improved cation permeable
separator suitable for use in an electrolytic cell. The separator
is reinforced with supporting fibers which are initially contained
in a fabric which also contains sacrificial fibers which are
subsequently removed from the fabric. The sacrificial fibers allow
a decrease in the amount of support fibers necessary for uniform
reinforcement of the separator.
Improved results in the electrolysis of brine have been found with
use of the reinforced cation permeable separator positioned between
an anode and cathode compartment in an electrolytic cell. More
specifically, an increase in electrical efficiency and/or a
decrease in voltage has resulted.
DETAILED DESCRIPTION
The cation permeable separator of the present disclosure contains a
polymer with ion exchange sites in which reinforcement is necessary
to increase the strength of the separator. Convetionally, the
separator will contain the polymer in the form of a film with a
separator thickness of no more than 30 mils, preferably no more
than 20 mils and most preferably less than 12 mils. Due to the
thinness of the polymer film, additional strength is necessary
through supporting fibers.
A relatively large number of supporting fibers in the cation
permeable separator is not desired since decreased electrical
efficiency and/or increased voltage has been found to occur in
operation of an electrolytic cell in comparison to the use of
separators which contained fewer supporting fibers.
The employment of a small number of supporting fibers in a fabric
of a loose or open weave or knit has proven unsatisfactory with
shifting of the fibers relative to one another prior to the fibers
being anchored or embedded as the reinforcing material. The
nonuniformity in the reinforcement with bunching of the fibers is
undesirable.
An additional effect has been observed by reinforcement with only a
relatively small number of supporting fibers; namely, the surface
of the cation permeable separator is not as smooth and flat in
comparison to a separator containing a greater number of these
fibers. After lamination to embed or anchor the supporting fibers,
peaks and valleys may be seen on the surface of the separator with
peaks outlining the position of the supporting fibers. A large
number of reinforcing fibers tends to minimize the distance between
peaks and valleys.
If the surface of the separator is not smooth and flat such as with
a corrugated surface, bubbles may accumulate during electrolysis
and act as an insulator. This effect has been observed in the
corrugations on a surface of a separator facing the cathode
compartment of an electrolytic cell. In the present disclosure it
is desired to produce a similar effect as results with the use of a
large number of supporting fibers and yet at the same time reduce
the amount of supporting fibers needed to reinforce the
separator.
The reinforcement for the cation permeable separators disclosed
herein includes supporting fibers which are initially contained in
a fabric which also contains sacrificial fibers which are
subsequently removed, e.g. by chemical destruction or by leaching.
The sacrificial fibers are woven or knitted into the fabric and
physically prevent the slippage of the supporting fibers. Prior to
use as the reinforcement, the fabric may be handled in normal
fashion without consideration to the type of knit or weave or the
type and amount of supporting fibers which are present. By
anchoring or embedding within a polymer matrix, the fabric
initially employed as the reinforcement, slippage of the supporting
fiber does not occur and the fibers do not move relative to one
another. Additionally, the surface of the polymer can have the same
degree of smoothness and flatness as if a greater number of
supporting fibers were employed. Thereafter, the sacrificial fibers
are removed resulting in a decrease in the amount of reinforcing
fibers in the separator.
In the present disclosure "sacrificial fibers" are defined to mean
fibers which can be removed without a detrimental effect on either
an intermediate polymer which is a precursor to a polymer
possessing ion exchange sites or a polymer with ion exchange sites.
The sacrificial fibers are removed from either polymer leaving
voids without interfering with the ion exchange capability of the
final polymer. The manner of removal of the sacrificial fibers
should not affect the supporting fibers employed to reinforce the
separator.
The sacrificial fibers may be made from a number of suitable
materials, e.g., synthetic polymers such as nylon, and cellulosic
materials, e.g. cotton and rayon. The primary requirement of the
sacrificial fibers is their removal without a detrimental effect on
the polymer matrix. With this proviso, the chemical makeup of the
sacrificial fibers is not critical. In similar fashion the manner
of removal of the sacrificial fibers is not critical as long as
this removal does not interfere with the ion exchange capability of
the final polymer in the cation permeable separator. For purposes
of illustration, removal of sacrificial fibers of a cellulosic
material such as rayon may be done with sodium hypochlorite.
The support fibers for reinforcement of the cation permeable
separator may be made from conventional materials since their main
purpose is to strengthen the separator. In lamination elevated
temperatures such as between 240.degree. to 320.degree. C. are
employed to embed the reinforcing material in an intermediate
polymer and the support fibers should also be able to withstand
these temperatures.
The cation permeable separator may be used in electrolysis to
produce highly corrosive chemicals and the support fibers must
withstand chemical attack. In the case of electrolysis of brine,
the reinforcing fiber should withstand exposure to chlorine and
caustic soda. Due to their chemical inertness, perfluorinated
polymers have been found to be highly desirable. The polymers
include those made from tetrafluoroethylene, tetrafluoroethylene
and hexafluoropropylene, and copolymers of tetrafluoroethylene and
perfluoro(alkyl vinyl ether) with an alkyl of 1 to 10 carbon atoms
such as perfluoro(propyl vinyl ether). Supporting fibers of
chlorotrifluoroethylene polymers are also useful.
The intermediate polymer which serves as the precursor to the
polymer containing ion exchange sites is prepared from monomers
which are fluorine-substituted vinyl compounds. The polymers
include those made from at least two monomers with at least one of
the monomers coming from each of the two groups described below.
The first group comprises fluorinated vinyl compounds such as vinyl
fluoride, hexafluoropropylene, vinylidene fluoride,
trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl
ether), tetrafluoroethylene and mixtures thereof.
The second group is the sulfonyl containing monomers containing the
precursor --SO.sub.2 F or --SO.sub.2 Cl. One example of such a
comonomer is CF.sub.2 =CFSO.sub.2 F. Additional examples can be
represented by the generic formula CF.sub.2 =CFR.sub.f SO.sub.2 F
wherein R.sub.f is a bifunctional perfluorinated radical comprising
2 to 8 carbon atoms. The particular chemical content or structure
of the radical linking the sulfonyl group to the copolymer chain is
not critical and may have fluorine, chlorine or hydrogen atoms
attached to the carbon atom to which is attached the sulfonyl
group, although the carbon atom must have at least one fluorine
atom attached. If the sulfonyl group is attached directly to the
chain, the carbon in the chain to which it is attached must have a
fluorine atom attached to it. The R.sub.f radical of the formula
above can be either branched or unbranched, i.e., straight chained
and can have one or more ether linkages. It is preferred that the
vinyl radical in this group of sulfonyl fluoride containing
comonomers be joined to the R.sub.f group through an ether linkage,
i.e., that the comonomer be of the formula CF.sub.2 =CFOR.sub.f
SO.sub.2 F. Illustrative of such sulfonyl fluoride containing
comonomers ##STR1##
The most preferred sulfonyl fluoride containing comonomer is
perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride), ##STR2##
The sulfonyl containing monomers are disclosed in such references
as U.S. Pat. No. 3,282,875 to Connolly et al. and U.S. Pat. No.
3,041,317 to Gibbs et al., U.S. Pat. No. 3,560,568 to Resnick and
U.S. Pat. No. 3,718,627 to Grot.
The preferred intermediate copolymers are perfluorocarbon, i.e.
perfluorinated, although others can be utilized as long as there is
a fluorine atom attached to the carbon atom which is attached to
the sulfonyl group of the polymer. The most preferred copolymer is
a copolymer of tetrafluoroethylene and
perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) which
comprises 10 to 60 percent, preferably 25 to 50 percent by weight
of the latter.
The intermediate copolymer is prepared by general polymerization
techniques developed for homo- and copolymerizations of fluorinated
ethylenes, particularly those employed for tetrafluoroethylene
which are described in the literature. Nonaqueous techniques for
preparing the copolymers of the present invention include that of
U.S. Pat. No. 3,041,317, to Gibbs et al. by the polymerization of
the major monomer therein, such as tetrafluoroethylene, and a
fluorinated ethylene containing sulfonyl fluoride in the presence
of a free radical initiator, preferably a perfluorocarbon peroxide
or azo compound, at a temperature in the range of
0.degree.-200.degree. C. and at pressures in the range 1-200 or
more atmospheres. The nonaqueous polymerization may, if desired, be
carried out in the presence of a fluorinated solvent. Suitable
fluorinated solvents are inert, liquid, perfluorinated
hydrocarbons, such as perfluoromethylcyclohexane,
perfluorodimethylcyclobutane, perfluorooctane, perfluorobenzene,
and the like.
Aqueous techniques for preparing the intermediate copolymer include
contacting the monomers with an aqueous medium containing a
free-radical initiator to obtain a slurry of polymer particles in
non-water-wet or granular form, as disclosed in U.S. Pat. No.
2,393,967 to Brubaker, contacting the monomers with an aqueous
medium containing both a free-radical initiator and a telogenically
inactive dispersing agent, to obtain an aqueous colloidal
dispersion of polymer particles, and coagulating the dispersion, as
disclosed, for example, in U.S. Pat No. 2,559,752 to Berry and U.S.
Pat. No. 2,593,583 to Lontz.
Conversion of the intermediate polymer to a polymer containing ion
exchange sites is by conversion of the sulfonyl groups (--SO.sub.2
F or--SO.sub.2 Cl). The converted polymer is a fluorine-containing
polymer with a plurality of sulfonyl groups present as ion exchange
sites. These ion exchange sites will be contained in side chains of
the polymer and will be attached to individual carbon atoms to
which are attached at least one fluorine atom. Conversion of all or
substantially all sulfonyl groups in the intermediate polymer to
ion exchange sites is not necessary. This conversion may be in
accordance with known techniques in the prior art, e.g., U.S. Pat
No. 3,770,567 to Grot and U.S. Pat. No. 3,784,399 to Grot. Sulfonyl
groups contained in the intermediate polymer can be converted to
ion exchange sites present as --(SO.sub.2 NH).sub.n Q where Q is H,
NH.sub.4, cation of an alkali metal or cation of alkaline earth
metal and n is the valence of Q or to the form --(SO.sub.3).sub.n
Me where Me is a cation and n is the valence of the cation.
Additional teachings of suitable ion exchange sites include the
disclosures found in U.S. Pat. Ser. No. 406,361 filed Oct. 15, 1973
and U.S. Ser. No. 425,079 filed Dec. 17, 1973. For purposes of
illustration the sulfonyl groups in the intermediate polymer may be
reacted with a mono-, di-, or polyamine.
The fabric containing the sacrificial fibers and supporting fibers
can be embedded within the separator in accordance with known
methods. Conventionally, the fabric will first be embedded within
or laminated into the intermediate polymer which is melt
fabricable. Temperatures of 240.degree. to 320.degree. C. are
suitable to embed the fabric in the intermediate polymer. A
disclosure for a suitable technique is found in U.S. Pat. No.
3,770,567 to Grot.
After the fabric is embedded within the intermediate polymer,
conversion of at least a portion of the sulfonyl groups to ion
exchange sites is desirably undertaken. Although the sacrificial
fibers may be removed prior to or at the time of conversion of the
sulfonyl groups of the intermediate polymer to ion exchange sites,
generally the removal will be subsequent to conversion of sulfonyl
groups. The sacrificial fibers may remain in the separator until
actual use in an electrolytic cell. In electrolysis of brine, the
sacrificial fibers will be destroyed if made from nylon, rayon and
the like. The removal of sacrificial fibers results in voids
present in the separator.
The cation permeable separators useful herein fall into two general
classes 1) separators which prevent any substantial hydraulic flow
of liquid through the separator, and 2) microporous separators
which allow liquid to hydraulically flow through the separator due
to pores contained therein. The general types of separators and the
manner of operation in an electrolytic cell is known and suitable
disclosures in the prior art are set forth in U.S. Pat. Nos.
3,773,634 to Stacey; 3,775,272 to Davis; 3,863,226 to Spitzer and
OS 2,243,866 to Darlington et al.
An improvement in use of a cation permeable separator in
electrolysis of brine has been found to occur as evidenced by a
reduction in voltage and/or an increase in electrical efficiency in
operation of an electrolytic cell. The beneficial results from
either of these characteristics directly translates into decreased
power consumption for each unit of production, e.g. caustic soda
and chlorine in the electrolysis of brine. With an improvement in
electrical efficiency, an additional beneficial result is in the
purity of the product produced. In a cell for electrolysis of brine
employing a cation permeable separator which prevents any
substantial hydraulic flow of liquid, hydroxyl ions will penetrate
into the anode compartment and react with chlorine. With an
increase in electrical efficiency, the number of hydroxyl ions
which penetrate into the anode compartment will be reduced. With a
microporous separator, anolyte flows through the separator to the
cathode compartment. With an increase in cell efficiency, fewer
impurities will be present in the caustic soda.
To account for the improvement in results in operation of an
electrolytic cell but without being desired to be bound to any
theory, the following explanation is given. A minimum amount of
reinforcing fiber is necessary to impart strength and mechanical
integrity to the cation permeable separator. The reinforcing fibers
(particularly for separators which are substantially impervious to
hydraulic flow) increase resistance to the flow of cations through
the separator. The cations flow freely where windows exist in the
separator, i.e., areas across the thickness of the separator where
no reinforcing material is present. Increased resistance to flow of
cations occurs where the supporting fibers are present since these
fibers do not contain ion exchange sites. The reduction in the
amount of reinforcing material means the overall area of windows is
increased and translates into increased electrical efficiency
and/or decreased voltage.
The removal of the sacrificial fibers leads to voids which do not
provide a path for substantial hydraulic flow in separators which
are substantially impervious to hydraulic flow with stagnant liquid
accumulating in the voids.
With microporous cation permeable separators, a reduction in the
amount of reinforcing material is also desirable. The maximization
of windows for flow of cations across the separator is less
critical. The separator has an inherently higher conductivity due
to pores which are filled with a highly conductive anolyte. With
microporous cation permeable separators the voids remaining after
removal of the sacrificial fibers are highly desirable and these
voids will be present both above and below the reinforcing fibers
and will crisscross these fibers. The voids provide paths for
optimum hydraulic flow of liquid around the reinforcing fibers and
at the same time provide paths for increased current conductivity
within the separator. Also, these voids after removal of the
sacrificial fibers aid in the hydraulic flow of liquid which pushes
back hydroxyl ions which would otherwise penetrate the separator
and react as an impurity in the anode compartment. A flow of liquid
directly across the width of the separator is undesirable since the
optimum combination of optimum hydraulic flow and electrical
conductivity is not present. In contrast, the pattern of voids left
by removal of the sacrificial fibers permits the flow of anolyte in
a path transverse to the width of the separator allowing a longer
path of intersection with electrical current.
Although in the present disclosure, advantages have been set forth
in the electrolysis of brine, the cation permeable separator can be
generally employed in electrolytic cells including those used for
electrolysis of alkali or alkaline earth metal halide
solutions.
To illustrate the present invention, the following examples are
provided.
EXAMPLES 1 and 2
In this and the following examples an intermediate polymer is
employed of a copolymer of tetrafluoroethylene and ##STR3## The
equivalent weight of the polymer is given and is the weight of the
polymer in grams containing one equivalent of potential ion
exchange capacity.
A 7 mil film of 1200 equivalent weight intermediate polymer was
surface-treated with ethylenediamine to a depth of 0.9 mils. Two
portions of the film were then vacuum laminated to the following
two reinforcements:
1. A fabric consisting in both warp and fill of 14 threads per inch
200 denier Teflon polytetrafluoroethylene yarn and 56 threads per
inch 50 denier rayon. This fabric was 6 mils thick.
2. As a control, a fabric was made by Stern & Stern Textiles
(pattern T-12). This fabric consists of approximately 40 threads
per inch 400 denier Teflon tetrafluoroethylene yarn in both warp
and fill, and is approximately 10 mils thick.
After lamination, the two samples were treated with a hot solution
of potassium hydroxide in aqueous dimethylsulfoxide to convert
remaining --SO.sub.2 F groups to --SO.sub.3 K groups.
After the two laminated samples were removed from the hydrolysis
bath, they were then soaked for one-half hour in dilute
(.about.10%) sodium hydroxide. They were then mounted in turn in a
laboratory electrolytic chlor-alkali cell. The electrodes used were
a dimensionally stable anode from Electrode Corporation and a
perforated stainless steel sheet cathode. The spacings between the
laminated samples and each electrode were approximately one-eighth
inch. Thin (.about.one-sixteenth inch) sheets of neoprene closed
cell sponge were used as gasket materials.
During the two electrolysis examples, a salt solution made up of
160 g NaCl/liter of solution, 0.25 ml of concentrated HCl/liter of
solution, and 0.022 g of sodium phosphate monobasic (NaH.sub.2
PO.sub.4.sup.. H.sub.2 O)/liter of solution was fed continuously to
the anode compartment. Outlet salt concentration was 135 g.
NaCl/liter of solution. To the cathode compartment was added at the
beginning of each example sufficient 10 N sodium hydroxide to fill
the compartment. After that, nothing more was added to the cathode
compartment throughout the duration of each electrolysis
experiment.
As the cell was being heated to its final operational temperature
of 80.degree. C., the current density was gradually increased to
its final value of 2 amperes/square inch. The cell was then run
continuously at 80.degree. C. and 2 amperes/square inch for several
days, and then the cell efficiency was measured by comparing the
amount of current passed through the cell. The results were as
follows:
______________________________________ Cell Ef- Normality ficiency
After Cell of Caustic Example 2 Days Voltage Produced
______________________________________ 1) Laminate formed with
Teflon/Rayon Fabric 82% 5.10 v 11.8 N 2) Laminate formed with T-12
Cloth (Control) 82% 5.63 v 11.6 N
______________________________________
Examination of Example 1 after removal from the cell revealed that
the rayon had been destroyed during the electrolysis.
EXAMPLES 3 and 4
Two fabrics as described in Examples 1 and 2 were individually
vacuum laminated to form a composite film of 4 miles of 1100
equivalent weight intermediate polymer and 1.5 mils of 1500
equivalent weight intermediate polymer. The fabric was contained in
the 1100 equivalent weight polymer. After lamination, the sulfonyl
groups of the intermediate polymer were converted to SO.sub.3 K
groups as described in Examples 1 and 2 followed by a treatment
with a hot solution of sodium hypochlorite which destroys the rayon
of Example 3.
After the two laminated samples were removed from the hydrolysis
bath, they were boiled for one-half hour in distilled water. They
were then mounted in a laboratory chlor-alkali cell similar to that
in Example 1.
During the two electrolysis experiments, a salt solution of 25% by
weight salt was fed continuously to the anode compartment. To the
cathode compartment was added sufficient 5.5 N sodium hydroxide to
fill the compartment. After that, sufficient distilled water was
fed into the cathode compartment during each electrolysis
experiment to maintain the catholyte normality at about 5.5-5.6
N.
After three days of operation at 80.degree. C. and 2 amperes/square
inch, the cell efficiency was measured by comparing the amount of
sodium hydroxide produced with the amount of current passed through
the cell. The results are as follows:
______________________________________ Cell Normality Efficiency
Cell of Caustic Example After 3 Days Voltage Produced
______________________________________ 3) Laminate formed with 1.5
mils 1500 EW film, 4 mils 1100 EW film, and Teflon / rayon fabric
73% 3.8 v. 5.6 N 4) Laminate formed with 1.5 mils 1500 EW film, 4
mils 1100 EW film, and T-12 cloth (Control) 70% 4.3 v. 5.5 N
______________________________________
EXAMPLE 5
A microporous separator was formed by lamination of the following
stack of materials in a vacuum laminator at approximately
280.degree. C. for two minutes: offset printing paper (top),
unfilled paper (nine pound weight) two plies facial tissue, 7 mil
of 1200 equivalent weight intermediate polymer, one ply facial
tissue, the Teflon/rayon fabric of Example 1, two plies facial
tissue, unfilled paper (nine pound weight), 10 mil blotter paper
(bottom). After lamination, the intermediate polymer had penetrated
all five plies of facial tissue but had just barely touched the
unfilled paper. The laminate was hydrolyzed in a solution of
potassium hydroxide in aqueous dimethylsulfoxide and the paper and
rayon destroyed by treatment with a hot solution of sodium
hypochlorite.
The separator was then boiled for one hour in distilled water.
While wet, it was mounted in a laboratory chlor-alkali cell similar
to that of Example 1. In this case, however, the cell was fitted
with a riser pipe such that the anolyte had a 161/2 inch hydraulic
head relative to that of the catholyte, and saturated brine was
used as the anolyte feed.
To the cathode compartment was added sufficient 2 N NaOH to fill
the compartment. No additional material was added to the cathode
compartment for the duration of the experiment.
As the cell was heated to its final operating temperature of
80.degree. C., the current density was gradually increased to its
final value of 1 ampere/square inch. The cell was then run
continuously for several days. At that point the current efficiency
was measured by comparing the amount of sodium hydroxide produced
with the amount of currency passed through the cell. The results
were as follows:
______________________________________ Normality of Caustic
Produced Cell Efficiency Cell Voltage
______________________________________ 4.5 N 98.1% 3.45 v 5.1 N
97.4% 3.47 v ______________________________________
EXAMPLES 6 and 7
A portion of the unhydrolyzed laminate from Example 5 was then
heated a second time under laminating conditions (15 minutes at
270.degree. C.) to obtain a deeper penetration of the polymer into
the paper. The sheet was then chemically treated as in the previous
example. The resulting separator was then boiled in distilled water
and mounted in the same laboratory chlor-alkali cell. Both the cell
startup and cell operation were as described in Example 5. After
several days of operation, the results were as follows:
______________________________________ Normality of Caustic
Produced Cell Efficiency Cell Voltage
______________________________________ Example 6) 4.7 N 96.6% 3.19
v 4.9 N 98.1% 3.17 v ______________________________________
Similarly, a separator was made in accordance with the procedures
of Example 6 with the substitution of the T-12 fabric of Example 2.
The remaining remarks of operating procedure made in reference to
Example 6 apply to Example 7. The results of the control were as
follows:
______________________________________ Normality of Caustic
Produced Cell Efficiency Cell Voltage
______________________________________ Example 7)(Control) 4.3N
89.7% 3.18 v ______________________________________
EXAMPLES 8 and 9
A microporous separator was formed by lamination of the following
stack of materials in a vacuum laminator at approximately
280.degree. C. for two minutes: offset printing paper (top), two
plies facial tissue, 7 mil of 1200 equivalent weight intermediate
polymer, one ply facial tissue, the Teflon/rayon fabric of Example
1, two plies facial tissue, 10 mil blotter paper (bottom). The
laminate was hydrolyzed in a solution of potassium hydroxide in
aqueous dimethylsulfoxide and the paper and rayon destroyed by
treatment with a hot solution of sodium hypochlorite.
The separator was then boiled for one hour in distilled water.
While wet, it was mounted in a laboratory chlor-alkali cell similar
to that of Example 1. In this case, however, the cell was fitted
with a riser pipe such that the anolyte had a 161/2 inch hydraulic
head relative to that of the catholyte, and saturated brine was
used as the anolyte feed.
To the cathode compartment was added sufficient 2 N NaOH to fill
the compartment. No additional material was added to the cathode
compartment for the duration of the experiment.
As the cell was heated to its final operating temperature of
80.degree. C., the current density was gradually increased to its
final value of 2 ampere/square inch. The cell was then run
continuously for several days. At that point the current efficiency
was measured by comparing the amount of sodium hydroxide produced
with the amount of current passed through the cell. The results
were as follows:
______________________________________ Normality of Caustic
Produced Cell Efficiency Cell Voltage
______________________________________ Example 8) 5.3 96.8 3.92
______________________________________
Similarly as in Example 8 a separator was made except for
substitution of a T-12 polytetrafluoroethylene cloth for the rayon
containing fabric operation in the chlor-alkali cell of Example 9
gave the following results:
______________________________________ Normality of Caustic
Produced Cell Efficiency Cell Voltage
______________________________________ Example 9) (Control) 5.0 N
79.5% 4.0 v ______________________________________
* * * * *